UV(IUE) spectra of hot post-AGB candidates

Abstract

Analysis of the low resolution UV(IUE) spectra (1150 to 3200 Å) of 15 hot post-AGB candidates is presented. The UV(IUE) spectra of 10 stars suggest partial obscuration of the hot stars due to circumstellar dust. The reddened continua of these 10 stars were used to model and estimate the circumstellar extinction. The circumstellar extinction law was found to be linear in lambda -1 in the case of IRAS 13266-5551 (CPD-55 5588), IRAS 14331-6435 (Hen3-1013), IRAS 16206-5956 (SAO 243756), IRAS 17074-1845 (Hen3-1347), IRAS 17311-4924 (Hen3-1428), IRAS 18023-3409 (LSS 4634), IRAS 18062+2410 (SAO 85766), IRAS 18371-3159 (LSE 63), IRAS 22023+5249 (LSIII +5224) and IRAS 22495+5134 (LSIII +5142). There seems to be no significant circumstellar extinction in the case of IRAS 17203-1534, IRAS 17460-3114 (SAO 209306) and IRAS 18379-1707 (LSS 5112). The UV(IUE) spectrum of IRAS 12584-4837 (Hen3-847) shows several emission lines including that of HeII. It may be a massive young OB-supergiant or a low mass star in the post-AGB phase of evolution. IRAS 16206-5956 (SAO 243756) and IRAS 18062+2410 (SAO 85766) show variability in the UV which in addition to stellar pulsations may be attributed to a dusty torus in motion around the hot central stars. The UV spectrum of the bipolar PPN, IRAS 17423-1755 (Hen3-1475) indicates that the central B-type star is obscured by a dusty disk. The stars were placed on the log g-log Teff diagram showing the post-AGB evolutionary tracks of Schönberner. Terminal wind velocities of the stars were estimated from the CIV and NV stellar wind features. The presence of stellar wind in some of these stars indicates ongoing post-AGB massloss.